Enhanced formation of stereocomplex crystallites in Poly(l-lactic acid)/Poly(d-lactic acid) blends by silk fibroin nanodisc

Abstract

Blending of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) is known to form stereocomplex crystallites (SC). In this research, the impact of a biobased filler, silk fibroin nanodisc (SFN), on the crystallizability of the PLLA/PDLA (50/50) blend was examined by differential scanning calorimetry (DSC), polarizing optical microscope (POM), and time-resolved small- and wide-angle X-ray scattering (SWAXS) measurements. The crystallization temperature (Tc), measured by non-isothermal DSC cooling scan, was increased by the addition of 1% SFN in the PLLA/PDLA (50/50) blend. The inclusion of SFN enhanced the formation of SC, as indicated by increasing the melting enthalpy of SC. Isothermal crystallization study at 110 °C by DSC and WAXS suggested that the SFN enhanced the SC crystallization while it suppressed the homocrystal (HC) crystallization, as indicated by crystallization half-time (t0.5) values. It was found that SFN not only enhances the SC crystallizability but also increases the fraction of SC crystals in the PLLA/PDLA blend. The long period of HC and SC lamellar stack was reduced by the addition of SFN, as indicated by the SAXS results. The POM results suggested that SFN significantly enhanced the number of SC nuclei for the isothermal crystallization at 170 °C from the melt.